Composite body and production process

ABSTRACT

A composite in which a substrate body is coated with a single layer or multiple layers and at least one layer has two or three phases comprised of cubic ZrCN and monoclinic or tetragonal ZrO 2 . The composite can be in the form of a lathe or milling cutter cutting insert.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/DE 97/02889 filed Dec. 10,1997 and based upon German national applications 197 01 863.7 of Jan.21, 1997, 197 09 300.0 of Mar. 7, 1997 and 197 37 470.0 of Aug. 28, 1997of the International Convention.

FIELD OF THE INVENTION

The invention relates to a composite body which is comprised of asubstrate body with a monolayer or multilayer coating.

The invention relates further to a process for producing a layer on asubstrate body of a hard metal, cermet or a ceramic.

BACKGROUND OF THE INVENTION

The first coatings, according to the state of the art, which allowed animproved wear prevention against free surface wear to be obtained, werecomprised of titanium carbide with a thickness up to 8 μm. Further,double or multiple coatings of titanium carbide and titanium nitride,especially with titanium nitride as an outermost layer, are known in theart for reduced cratering when the product is used as a cutting insertin machining. For further improvement of such cutting inserts,multilayer coatings of the layer sequence TiC, Ti(C,N), TiN, have beenproposed. It has been found that the natural brittleness of ceramics,like Al₂O₃ can be minimized when Al₂O₃ is applied in a thin layer formand thus, TiCTi(C,N) and an outer layer of Al₂O₃ have been provided asmultiple coatings. While the patent literature, for example EP 0 299 282B1 describes in special cases the use of carbides, nitrides and/orcarbonitrides of the elements titanium, zirconium, hafnium, vanadium,niobium and/or tantalum, these have been described only as useful in anexample with titanium compounds as coating materials, in part incombination with aluminum oxide. The same is true with the descriptionof ZrO₂ in the combination with or as a replacement for oxide coatings.DE 36 20 901 A1 or EP 0 250 865 A1 which has the same content, describesfor the first time a cutting tool whose cutting edge is coated withtitanium carbide, titanium carbonitride and/or titanium nitride andwhose outermost cover layer is composed of a thin zirconium nitridelayer. The zirconium nitride, which has poorer wear characteristics thanthe aforementioned titanium compounds should hinder the oxidation of thebase layer underlying this coating by atmospheric oxygen, whereby thegood wear characteristics of the titanium carbide, titanium carbonitrideand/or titanium nitride coatings can be fully maintained.

By contrast, in U.S. Pat. No. 3,854,991 (or CH A 585273) a coating of asintered hard metal product is described in which the coating iscomprised of HfCN and/or ZrCN and has an X-ray diffraction latticeconstant which in the case of HfCN and a mixture of HfCN and ZrCN liesbetween 4.5570 and 4.630 angstrom and in the case of ZrCN lies between4.6 and 4.62 angstrom. In the case of ZrCN the CN ratio is clearly lessthan 1. For the production of these hafnium or zirconium carbonitrides,a hafnium halogenide and/or a zirconium halogenide can be fed over asubstrate together with hydrogen, nitrogen and a hydrocarbon at atemperature of 1000 to 1300° C.

U.S. Pat. No. 4,714,660 describes a cutting insert of a CVD-coatedsubstrate body in which the first CVD layer is comprised of at least twophases deposited simultaneously together, of which the first is composedof a member of the group of carbides, carbonitrides, nitrides,oxycarbides, oxycarbonitrides, suicides or borides of titanium,zirconium, hafnium, vanadium, niobium or tantalum, or a carbidesilicideor boride of chromium, molybdenum or tungsten, or a silicon or boroncarbide and a second of these phases is selected from the group ofoxides or oxynitrides of aluminum, titanium, zirconium, hafnium,magnesium, silicon and calcium or very stabilized zirconium oxide.

Of the deposited mentioned phases, at least one of the phases iscomposed of fibers, spikes or column-shaped particles with an elongatedaxial orientation extending in a direction which is perpendicular to thesubstrate/coating surface of the composite.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a composite body ofthe type described at the outset which has a high microhardness, goodwear characteristics, especially in chip removal machining operationslike turning or milling, or hard abrasively loaded wear hardness.

SUMMARY OF THE INVENTION

This object is achieved with the composite body which, according to theinvention, is characterized in that at least one layer has two or threephases which are comprised of cubic ZrCN and monoclinic and/ortetragonal ZrO₂.

In the CVD deposition of TiCN, when oxygen is contained in the gasatmosphere, it is incorporated in the (single phasic) lattice wherebyTi(C,O,N) deposits result. The presence of oxygen in the gas phaseresults in the deposition of two adjoining phases in the coating,namely, ZrCN and ZrO₂ when certain boundary conditions are maintained.This can be expected from the chemical similarity of zirconium andtitanium, which both are from the same group of the periodic system,along with good adherence of the resulting coating on the substrate bodyor on another layer or as an intermediate layer. The new coating hasbeen found even with composite bodies which are formed as cuttinginserts, to give rise to significant improvements in the useful life ofthe insert in the milling of steel. The useful life, e.g. as a steelmilling insert, can be increased by about 30%. Further this coating issuitable in a significant manner for the efficiency improvement ofdeformation shaping tools which are subject to friction wear.

Thickness of the layer according to the invention should be between 2and 10 μm, preferably at least 3 μm. Based on the differentcharacteristics of the ZrCN on the one hand and the ZrO₂ on the other,known in the art, which can be advantageously used, it is another basicthought of the invention established in the layer a gradient of therelative ZrO₂/ZrCN proportions. Depending upon the desired boundaryzone, for example, the ZrO₂ content in the layer can decrease outwardly.For example for the machining of castings, a higher ZrCN content isadvantageous whereas in the use of a ZrCN/ZrO₂ layer as an outer layeror a single layer for cutting inserts which are to be used for machiningcastings, the ZrO₂ relative content toward the exterior can be decreasedpreferably to zero. Conversely the adhesion of ZrO₂ to substrate bodiesas well as to other layers is in part better than that of ZrCN so thatthe ZrO₂ component can increase inwardly, preferably to the boundarywith the substrate body, growing, for example up to 100%. The gradientadjustment can be carried out during the CVD coating by adjusting theCO₂ content as a function of time.

Apart from the aforedescribed boundary zones, it is preferred,especially with a two phase coating that there be a homogeneousdistribution of the relative mass proportions of ZrO₂ between 5 and 75mass %, preferably between 5 and 60% and most preferably between 20 and40%. The ZrO₂ proportion which is selected in the layer can be chosen inconsideration of the purpose for which the composite body is to be usedand set accordingly. Furthermore, the ratio of monoclinic to tetragonalZrO₂ can be varied via the coating geometry. Preferably this ratio is inthe range of (3 to 4):(7 to 6). Thus at a coating temperature of about950°, it is possible to obtain ⅔ of the ZrO₂ component as tetragonalZrO₂ in addition to the Zr(C,N) phase. At higher temperatures thetetragonal ZrO₂ proportion grows and can reach 100% at a coatingtemperature of about 1100° C. The ZrCN phase is present in cubic form.

The substrate body, upon which one or more layers can be coated, ofwhich one can be the coating of the invention, can be composed of hardmetal, cermet or a ceramic. The coating can be a multilayer coating andapart from the layer of ZrCN/ZrO₂ can comprise at least one layer of acarbide, nitride and/or carbonitride of an element from group IVa orGroup Va or group VIa of the periodic system, and optionally also acoating of Al₂O₃ and/or ZrO₂, whereby dioxide layers can form theoutermost layer and also a layer underlying the ZrCN/ZrO₂ layer whenthat is outermost. Finally a diamond-like layer can be used as the outerlayer. In a preferred use the outer layer is comprised of a ZrCN/ZrO₂layer under which an Al₂O₃ layer can be provided. Good wearcharacteristics on machining can also be obtained with the followinglayer sequence (given from inner side to outer side):

TiN: 0.5 to 2 μm, preferably up to 1 μm; TiCN: 2 to 5 μm, ZrCN/ZrO₂: 2to 10 μm.

Preferably the coating of the invention is composed of ZrCN and ZrO₂,optionally in combination with other layers of other compositions, isapplied by means of CVD deposition on a coated or uncoated substratebody composed of a hard metal, a cermet or a ceramic, at a temperaturebetween 800° and 950° with a Zr-halogenide in stoichiometric excess inthe gas phase, CO₂, hydrogen, and a material with a C—N group as acarbon and nitrogen donor at a pressure between 5 kPa and 100 kPa. ForCVD deposition, a Zr halogenide, especially ZrCl₄, in a stoichiometricexcess, CO₂, H₂ and a material with a C—N group as a carbon and nitrogendonor, are admitted at a pressure between 5 kPa and 100 kPa and at atemperature between 800° C. to 950° C. The stoichiometric excess of thezirconium halogenide is required to suppress the deposition of carbon(soot). The material serving as a C—N donor preferably has a cyanidegroup with a triple bond between the carbon and the nitrogen whose bondspacing at room temperature is between 0.114 and 0.118 nm. Suchcompounds can be hydrogen cyanide, cyanamide, cyanogen, cyanoacetylene,or acetonitrile. Alternatively or in part, such gaseous compounds canalso be used which have CN molecular groups with a simple bond betweenthe carbon and the nitrogen, like, for example, methylamine andethylenediamine. Basically also the compounds described in DE 25 05 009A1 can be used. Alternatively it is also possible to gate into thereaction vessel such materials which are capable of forming such cyanidegroups at the above-mentioned reaction temperatures. Preferably thecoating temperature, i.e. the temperature of the substrate body to becoated or the substrate body which has already been coated with one ormore layers, is between 900° C. and 920° C. In the course of thecoating, preferably the CO₂ proportion in the gas atmosphere is loweredso that the phase proportion of the ZrO₂ in the ZrCN/ZrO₂ layer isreduced progressively with time so that a gradient is formed in thelayer. By reducing the CO₂ proportion to 0, the ZrO₂ proportion can bereduced also to 0 in a corresponding way. Conversely, increasing the CO₂proportion and correspondingly decreasing the proportion of the C—Ndonor, the ZrO₂ proportion in the coating can be increased.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a perspective view of a cutting insert according to theinvention; and

FIG. 2 is a section along line A-B if FIG. 1, drawn to a larger scale.

SPECIFIC DESCRIPTION

FIG. 1 shows a cutting insert 10 whose cutting corner 11 is shown insection in FIG. 2 schematically in a cut taken along the line A-B inFIG. 1.

As can be seen from FIG. 2, a first 1 μm thick layer 13 of TiN, a second4 μm thick layer 14 of TiCN, a third 2 μm thick layer 15 of Al₂O₃ and anouter 3 μm thick cover layer 16 of ZrCN/ZrO₂ are applied to a substratebody 12 which is comprised of a WC hard metal with 6% cobalt as abinder.

In a further series of tests, 1000 lathe cutting plates with thedesignation CNMG 120412-49 of a substrate base body are coated. The hardmetal alloy serving as the substrate base body is comprised of 93.9 mass% WC and 6.1 mass % Co. The coating is carried out by the CVD process inan apparatus which permits temperature adjustment to 1100° C. andpressures between 5 kPa and 100 kPa. In the coating apparatus thefollowing gases can be introduced: hydrogen, nitrogen, carbon dioxide,methane, acetonitrile, titanium tetrachloride, zirconium tetrachlorideand aluminum trichloride.

Half of the substrate bodies were coated at 990° C. with a multilayercoating of the following individual layers:

Individual Layer Thickness (μm) Gases Used TiN 1.5 H₂, N₂, TiCl₄ Ti(C,N)4.5 H₂, N₂, CH₄, TiCl₄ Al₂O₃ 3.0 H₂, CO₂, AlCl₃ TiN 1.0 H₂, N₂, TiCl₄Total thickness   10.0 μm.

The aforementioned coating is known from the art. In a further coatingseries, the mentioned substrate bodies are provided at 990° C. with amultilayer coating of the following individual layers:

Individual Layer Thickness (μm) Gases Used TiN 1.5 H₂, N₂, TiCl₄ Ti(C,N)4.5 H₂, N₂, CH₄, TiCl₄ Zr(CN)/ZrO₂ 3.6 H₂, CH₃CN, CO₂, ZrCl₄ Totalthickness    9.6 μm.

In the first and second coating series, the first layer of TiN and thesecond layer of Ti(C,N) are in common. Only the outer layers aredifferent and in one case consist of an Al₂O₃ coating and an outer TiNlayer and in the case of the invention, of the layer according to theinvention of ZrCN and ZrO₂. The last-mentioned coating was analyzedwhereby with the aid of an optical microscope and a scanning electronmicroscope it was observed that with use of the reaction gases H₂, CH₃,CO₂ and ZrCl₄, the individual layers comprised two different phaseswhich could be determined by X-ray diffractometry to be cubic zirconiumcarbonitride and monoclinic zirconium oxide. This result is surprisingbecause normally with CVD deposition from gas mixtures whichtheoretically would be suitable for the deposition of two or morematerials, in practice only one material is deposited, namely the phasewhich is most thermodynamically stable. In further tests this has beenconfirmed by CVD deposition from a gas mixture of H₂, CH₄, N₂, CO₂ andZrCl₄. The deposited layer substantially consists of ZrO₂ and has ahardness less than that of the ZrCN/ZrO₂ coating of the invention. Thisshows that for the deposition of the coating according to the invention,the material with a C—N group as the carbon and nitrogen donor must bepresent.

According to the invention it is also possible to vary the gascomposition during the coating, for example by varying the proportionsof the relative gas contents CH₃CN/CO₂. In this manner, especially inthe lower part of the last layer, a greater proportion of ZrCN and inthe upper part an enrichment in ZrO₂ can be produced.

Each group of the aforementioned lathe cutting plates with the coatingTiN, Ti(C,N), Al₂O₃ and TiN, as representatives of state of the artcutting inserts, and those with a coating according to the invention ofTiN, Ti(C,N), Zr(C,N)/ZrO₂ are used to turn a shaft of a diameter of 300mm of a ductile steel composition X5CrNi1810 (stainless steel). Therespective cutting plates had total coating thicknesses which did notdiffer from one another by more than 0.4 μm. The following cuttingconditions applied:

Cutting speed v_(c) = 160 m/min Cutting depth a_(p) = 2 mm Feed f = 0.4mm/rotation.

With the cutting plates of the state of the art, cutting durations on anaverage of 12 minutes were obtainable. For the cutting plates of theinvention the cutting duration was 18.5 minutes on average. Theseresults showed that the cutting inserts according to the invention hadsignificantly better wear properties.

In a further example, a punching die was fabricated with an outercoating according to the invention of ZrCN and ZrO₂. This coating wasfound to provide a dry lubrication effect which was attributed to theeffect of ZrO₂ as a dry lubricant and was characterized by an especiallylow chemical affinity to metallic materials in shaping processes whichdid not involve chip removal.

In the production of valve stems for auto engines which were composed ofCo—Ni superalloy, the valve stems before shaping were heated to about600° C. and then introduced into a hard metal die of WC with 15 mass %cobalt. After about 10000 stampings, the die had to be repolished.

In a second procedure, the hard metal die of WC with 15 mass % cobaltwas coated with 1.5 μm TiN and 5 μm ZrCN/ZrO₂ in which the ZrO₂component was ⅖ in monoclinic form and ⅗ in tetragonal form. 124processed pieces showed that the die would require after polishing onlyafter 50000 operations. The coating of the invention thus showed thattools operating without chip removal also had a significantly improvedlife.

What is claimed is:
 1. A composite body comprised of a substrate bodywith a monolayer or multilayer coating wherein at least one layer hastwo or three phases comprised of a cubic ZrCN and monoclinic and/ortetragonal ZrO₂.
 2. The composite body according to claim 1 wherein saidat least one layer is a ZrCN/ZrO₂ layer having a thickness of at least 2μm.
 3. The composite body defined in claim 2 wherein said thickness is 3μm to 10 μm.
 4. The composite body according to claim 1 wherein said atleast one layer is a ZrCN/ZrO₂ and a mass ratio of ZrCN to ZrO₂ in theZrCN/ZrO₂ layer varies with distance from a boundary surface betweensaid body and said coating.
 5. The composite body according to claim 4wherein the ZrO₂ content of the ZrCN/ZrO₂ layer which is a single layeror the outermost layer, decreases outwardly.
 6. The composite bodydefined in claim 5 wherein the ZrO₂ content in said at least one layerdecreases outwardly to zero.
 7. The composite body according to claim 4wherein the ZrCN/ZrO₂ layer is a first of a plurality of layers or is anoutermost layer and has a ZrO₂ proportion increasing inwardly to 100%.8. The composite body according to claim 1 wherein a relative massproportion of the ZrCN/ZrO₂ phase in said coating is between 5 and 75mass %.
 9. The composite body defined in claim 8 wherein said relativemass proportion is between 15 and 60 mass %.
 10. The composite bodydefined in claim 9 wherein said relative mass proportion is between 20and 40 mass %.
 11. The composite body according to claim 1 wherein saidone layer has a ratio of monoclinic to tetragonal ZrO₂ of (3 to 4): (7to 6) and the ZrCN in said one layer is present in cubic form.
 12. Thecomposite body according to claim 1 wherein the substrate body iscomprised of hard metal, a cermet or a ceramic.
 13. The composite bodyaccording to claim 1 wherein the substrate body is coated with amultilayer coating and at least one layer of said coating is comprisedof carbides, nitrides and/or carbonitrides of an element from group IVa,group Va or group VIa of the periodic system and/or from Al₂O₃ and/orZrO₂ or a diamond-like layer.
 14. The composite body defined in claim 13wherein the oxide layer or the diamond-like layer is the outermost layerof said coating.
 15. The composite body according to claim 1, whereinsaid at least one layer of ZrO₂ and ZrCN is the outermost layer of saidcoating.
 16. The composite body defined in claim 15 wherein a layer ofAl₂O₃ underlies said outermost layer.
 17. The composite body accordingto claim 1, wherein said coating comprises a layer sequence from theinner side to the exterior of the substrate body with the followingthicknesses: TiN: 0.5 to 2 μm; TiCN: 2 to 5 μm; ZrCN/ZrO₂: 2 to 10 μm.18. The composite body defined in claim 17 wherein the TiN layerthickness is up to 1 μm.
 19. A process for producing a two or threephase containing layer on a coated or uncoated substrate body composedof a hard metal, a cermet or a ceramic, by means of a CVD deposition ata temperature between 800° C. to 950° C. with a Zr-halogenide instoichiometric excess in the gas phase, CO₂, hydrogen and a materialwith a C-N group as a carbon and nitrogen donor at a pressure between 5kPa and 100 kPa.
 20. The process according to claim 19 wherein the C—Nmolecular group is a cyanide group-CN with a triple bond between thecarbon and the nitrogen, whose bond spacing at room temperature isbetween 0.114 and 0.118 nm.
 21. The process defined in claim 20 whereinthe carbon and nitrogen donor is acetonitrile.
 22. The process accordingto claim 19 wherein the C—N molecular groups contain molecular groupingswith a simple bond between the carbon and the nitrogen.
 23. The processaccording to claim 19 wherein the coating temperature is between 900° C.and 920° C.
 24. The process according to claim 19, further comprisingvarying a CO₂ proportion in the gas phase during the coating time 4 forcreating a ZrO₂ concentration gradient in said layer.
 25. The processaccording to claim 19, further comprising varying a ratio of monoclinicto tetragonal ZrO₂ in said layer by adjustment of the coatingtemperature.